1. Melt butter in a large skillet over medium heat. Add onions and celery; cook 3 to 5 minutes, until soft. Transfer to a large bowl; stir in bread, salt, pepper and sage.
2. Drain oysters through a large strainer over a 1 quart glass measure; transfer oysters to a bowl. Strain oyster liquid through a fine sieve into a separate bowl; set aside. Rinse oysters under cold running water to remove any sand or shells, then coarsely chop. Add oysters to bowl with bread mixture.
3. Gently stir in oyster liquid, milk and egg, stirring just until all ingredients are combined.To stuff turkey::
4. Proceed as directed for The Perfect Turkey.
5. To bake: Heat oven to 325 degrees F. Spoon stuffing into a well-buttered 13x9x2-inch glass baking dish. Cover with foil and bake 30 minutes. Makes 15 (1/2-cup) servings.